1. Field of Invention
The invention relates to a holographic storage and regeneration system and in particular to a holographic storage and regeneration system having servo mechanism.
2. Related Art
Presently, in the market of optical storage medium, since the capacity of the commercialized blue-light CD can hardly exceed the threshold of 100 Gbytes, thus various kinds of potential ultra-high capacity data recording technologies are under intensive research and development, and among them, the holographic CD is the most promising choice. The research and development of holographic recording technology has had a long history, however, due to various reasons, it still has not been utilized in the consumer optical storage products. Taking it for an example, holographic experiments conducted in the early days must be carried out by utilizing an enormously voluminous high power laser light source of several hundredths of milli-watts as well as a complicated optical system, and moreover, they must be used in cooperation with a heavy shock-proof table. Furthermore, the Photo-Refractive Crystal utilized as the holographic recording medium is even more expensive and beyond the comparison of the ordinary-priced medium. However, along with the rapid progress and development of this technology, the restrictions originally imposed on the holographic storage and recording technology have already solved and removed one-by-one. For example, the following systems and devices have made tremendous progress in their technologies, such as miniaturized high power laser, high photo-sensitive recording medium, and miniaturized data access optical system having position servo functions, such that the conventional thinking that the recording medium must be capable of being overwritten is changed due to the change of consumer habit in the compact disk (CD) market. However, up to the present time, it is still a very difficult task for the recording medium of Photo-Refractive Crystal capable of being written repeatedly to be able to satisfy the requirement of excellent material characteristics, high data stability and inexpensive price. In recent years, due to the popularity and widespread utilization of ordinary-priced write-only-once CD-R/DVD-R, thus the recognition that the holographic recording does not have to strive for the medium material capable of being overwritten repeatedly has gained widespread acceptance. If the functional requirement of overwriting repeatedly is not taken into consideration, then there are plenty of cheap organic material having high photo sensitivity, that can be chosen and utilized as data recording layer for the holographic CD, for example, a photo polymer is one of them. Under strong irradiation of recording light, the photopolymer may produce molecular chain like chemical reactions, thus the change of optical properties caused by the characteristics of sparsity and density of the molecular chains can be used to record and regenerate data related to 3-dimensional holographic interference fringes. The concept of the afore-mentioned miniaturized data access optical system having position servo functions is originated from the servo mechanism of CD/DVD player, and that is the keypoint in realization the implementation of holographic CDs.
With regard to the technology of holographic storage, such as that as disclosed in Joint International Symposium on Optical Memory and Optical Data Storage 2005 (ISOM/ODS 2005), Hawaii, US, paper ThE2, that is realized through a transmissive type holographic recording medium, and in this configuration, a two dimension image sensor and a Spatial Light Modulator are placed on the same side of a Holographic Storage Medium. And in executing data regeneration, a set of reflection mirrors placed on another side of the Holographic Storage Medium must be controlled mechanically, so that the reference light produced in regeneration is incident on Holographic Storage Medium along a direction opposite to that of the reference light utilized in a data recording process, as such for Holographic Storage Medium in continuous motion, the position and direction of the set of reflective mirrors can not be corrected swiftly in a real-time manner.
In addition, another related prior art is disclosed in U.S. Pat. Gazette Publication No. 6,721,076 and U.S. Pat. No. 6,909,529, wherein, an optical framework used for reflective type holographic recording medium is disclosed in detail. However, for a displacement multiplex continuously moving Holographic Storage Medium, a concrete servo mechanism is lacking.
Moreover, in another USP 20040212859, a reflective and transmissive Holographic Storage approach is disclosed. Wherein, a servo light is incident onto a servo track of a Holographic Storage Medium through an object lens in an optical path, thus a servo mechanism of displacement multiplexing is utilized. However, its shortcomings are that, when performing angle multiplexing, the function of angular servo mechanism is lacking.